Electrophoretic display screens have many advantages for electronic reading devices because they are generally able to provide a thin and/or non-volatile display. The electrophoretic display medium may be driven by a backplane behind the electrophoretic medium. In some preferred devices the backplane is fabricated using solution based thin film transistors (TFTs), preferably patterned by techniques such as direct-write printing, laser ablation or photolithography. Further details can be found in the applicant's earlier patent applications, including, in particular, WO 01/47045, WO 2004/070466, WO 01/47043, WO 2006/059162, WO 2006/056808, WO 2006/061658, WO 2006/106365 (which describes a four or five layer pixel architecture) and PCT/GB2006/050265, all hereby incorporated by reference in their entirety. Thus, in embodiments, the TFTs comprise an organic semiconductor material, for example a solution processable conjugated polymeric or oligomeric material, and in embodiments the display screen, more particularly the backplane, is adapted to solution deposition, for example comprising solution-processed polymers and vacuum-deposited metals.
Image update of an electrophoretic display screen may result in a faint impression of the previous image remaining visible, i.e., “ghosting”. Such an impression may be avoided or attenuated by refreshing the screen several times, for example by firstly applying a frame(s) to set every pixel white, then a frame(s) to set every pixel black, then another frame(s) for the colours/grey levels of the desired image. Where such a display screen has a split backplane for example due to combining independent display panels, it is desirable to update the split backplane regions in parallel such that the updating involving successive frames can be performed more quickly. However, effects due to the split backplane may in this case become visually perceptible to the human eye.
For example, an electronic reading device may, in practice, comprise two or more physically independent display panels that have been butted together to create a single larger one. In such a reader device having correspondingly two or more backplanes, effects due to the multi-display panel construction may indicate to the user that the device in fact comprises more than one display panel and provide an undesirable visual distraction to said user.
The field of electronic reading devices therefore continues to provide a need for an improved display screen comprising a split overall backplane. Such improvement may have one or more advantages of, inter alia, creating a more visually pleasing reader experience and/or improving reliability of the screen, preferably avoiding or reducing any inconsistencies between the physically independent display panels of the screen, wherein such inconsistencies may for example degrade the reliability and/or result in undesirable visible performance issues.
Other devices are known from US2005/0275645 (Vastview Tech Inc), US2006/0279489 (Hitachi Ltd), EP1677276 (LG Philips LCD co Ltd), JP2001021865 (Matsushita Electric Ind Co Ltd) and U.S. Pat. No. 5,889,568 (Rainbow Displays Inc).